For Fourier Transform Mass Spectrometry (FTMS), the detection limit of mass-to-charge (m/z) ratio analysis has been defined in Marshall, A. G., Hendrickson C. L., “Fourier Transform Ion Cyclotron Resonance Detection: Principles and Experimental Configurations”, Int. J. Mass Spectrom. 2002, 215, 59-75. There, the detection limit is considered the minimum number of ions, M, of charge q detected with signal-to-noise ratio 3:1. This detection limit has been shown as proportional to the voltage noise of an input transistor of the pre-amplifier (Vn), the capacitance of the detection circuit (Cdet) and inversely proportional to the relative amplitude of detected oscillations, A. In other words,
  M  =      const    ⁢                  ⁢                            C          det                ⁢                  V          n                    qA      
The voltage noise is determined by the process of semiconductor manufacturing and improvement here is limited. Also, the relative amplitude of detected oscillations is limited by the quality of the trapping field and improvement here is also difficult (for example, in practical electrostatic orbital trapping analyzers, A is close to 60-70%). Therefore, an improvement to the detection limit is likely to be achieved by reducing the capacitance of the detection circuit, Cdet.
WO-2008/103970 shows a wideband pre-amplifier for FTMS. However, in this design, it is suggested that the signal-to-noise ratio is optimised when the input capacitance of the JFET transistor in the pre-amplifier is equal to the sum of the wiring capacitance and the capacitance of the detection plate. This is a different approach than the reduction in capacitance suggested above.
Reduction of the parasitic capacitance in mass analysers is typically implemented via passive measures, for instance by separating detection electrodes, reducing their size or making wires as short and thin as possible. All these methods provide only an incremental improvement. It is desirable to provide a significant reduction of multiple sources of capacitance using another method.